1. Field of the Invention
The present invention relates to a diaphragm valve made of plastic and suitably utilized in the food industry for controlling transportation of a liquid.
2. Description of the Prior Art
A diaphragm valve comprising a valve body provided on each side thereof with a body cap by means of a cap nut threadedly engaged thereto is well known in the art. This type of the disphragm valve usually has a sealing means between the valve body and the body caps consisting of an annular groove recessed on the end surface of the body or the caps and an O-ring engaged in the groove. Such a valve has the drawback that a small amount of liquid transported through the valve tends to remain in the gap between the annular groove and the O-ring or between the opposed end surfaces of the body and the caps. This remaining liquid may freeze and expand in the winter, causing loose sealing. The remaining liquid causes a further serious problem when the valve is applied in the food industry because it may putrefy by bacteria and contaminate the entire system. When the transported liquid is purified water, it may degrade the purity of the water.